The present invention relates to a composite patient support stretcher used to support patients during X-ray examinations, and, more particularly, to a polymeric resin strengthened fibrous shell with a balsa wood core support structure, and a method for forming the same.
The increasing application of X-ray medical procedures in lieu of such invasive techniques as surgery for examination, diagnosis or therapy, and the development of tomographic procedures (wherein X-rays of a predetermined plane section are made) to fulfill objectives which are unobtainable by conventional radiographical procedures have promoted the usage of accessory X-ray equipment having characteristics particularly suited for a specific application.
In conventional radiology, for example, the patient is subjected to radiation from an X-ray tube acting as a point source. The attenuation of the rays (reduction of power per unit area with distance from the source) through the thickness of the patient's body is recorded on a single film. Because it is desirable to limit the radiation dose (radiation per unit volume of body tissue), it is important to reduce the attenuation attributable to accessory equipment, such as patient support stretchers, which is interposed within the X-ray path, in order to reduce the required source intensity. Thus, a patient support as shown in U.S. Pat. No. 3,947,686 is described as having low X-ray attenuation (equivalent to 1 mm Al or less), in addition to minimal deflection under load when supported in a cantilevered position. The support therein is formed with a polyurethane foam core and a shell composed of graphite fiber embedded in polyurethane. For convenience the shells may be fabricated from prepregs. Prepregs are pre-engineered, ready to mold combinations of resin and reinforcement. U.S. Pat. No. 3,897,345 also describes a patient support designed for low attenuation purposes which is composed of a shell containing graphite or carbon fibers in a plastic resin matrix around and bonded to a rigid polyurethane core. Moreover, British Pat. No. 1,435,223 discloses the use of panels composed of cast resin reinforced with carbon fiber material that has a hard foam core sandwiched between the panels in an apparatus for subjecting a patient to X-ray or gamma-ray examination or therapy. The apparatus is characterized as having considerable mechanical strength, and low X-ray and gamma-ray absorption.
The shells of the prior art patient support stretchers are typically cured in a mold prior to bonding with the foam cores since application of the shell curing heat may be detrimental to the foam, particularly where polyurethane is used. The shells are subsequently bonded to the core. Thus, a multi-phase labor intensive procedure is required to form the stretchers, that is, separately molding the top shell and the bottom shell; trimming the shells; shaping the core; bonding the core to the bottom shell; and, bonding the top shell to the core-bottom sheel combination.
Since irregularities in stretcher density can appear as images on conventional radiographic photographs, allowable density variations are stringently limited in order to preclude interpretation thereof as a tumor.
Recently, tomographic procedures have been developed to provide images that reveal information which may be hidden from view in conventional radiographic diagnosis due to overlap of anatomical features. In computerized tomography, for example, an image of a cross-sectional plane of a specimen is developed by sequentially directing X-rays through the subject from a plurality of directions. In the basic scanning process, a collimated X-ray beam passes through the patient's body (and at some angles through the stretcher), is attenuated to varying degrees, and impinges on a sensor which detects the amount of radiation received and electronically converts it to a signal that may be recorded by a computer. Angular rotational movement of the radiation source is coordinated with that of the sensor. The patient typically is translated normal to the orbital plane defined by the rotation of the source-sensor pair. The X-ray profiles of each section are processed by the computer which can reconstruct the images that have been accumulated to depict cross sections of the body.
Since tomographic techniques are not as sensitive to density variations as conventional radiographic techniques, the stretcher does not require precision density homogeneity. Moreover, because the X-ray beam is well collimated, only the sections being scanned are irradiated and overall dose received for a complete scan of the section is comparable to the dosage received from a single conventional X-ray. Thus, the significance of low patient support stretcher attenuation is less critical than in conventional radiography. The combination of these factors is conducive to the use of core materials having medium attenuation but which can be more efficiently fabricated.